Atari-style joystick to PC joystick adapter

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​01 Mar 1998

connector or cable wiring scheme

9 pin D-SUB male connector to
the Atari joystick

15 pin D-SUB male connector
to the PC

Some games are easier to play with digital joystick instead of
analogue type. Unfortunately PC has only analogue joystick
connector, which makes it impossible to connect normal digital
joystick to it. But with a little adapter circuit, it is possible
to use Atari style digital joystick with IBM PC joystick interface.
The circuit adapts the joystick connectors and converts digital
joystick movement signals to analogue signals. The circuit can be
used with any PC game to replace the original analogue joystick.
The circuit also simulates also Gravis Gamepad operations except
the extra buttons.1,R3,R4,R6 2.2 kohm R2,R5 100
kohm T1,R2 BC557 D1,D2 1N4148 P1,P2 100 kohm trimmer Generally the
circuit is not very sensitive to the component differences on
diodes and transistors. Generally almost any small signal
transisotr with Hfe on range of 100-500 should do the job. For the
diode you can use almost any common diode, like very popular 1N4001
rectifying diode.

The circuit operation

The interface circuit directly connects the joystick buttons to
the corresponding PC joystick connector pins because they operate
similarly in both joystick types. Because PC need different
resistances to X and Y inputs to know the joystick position, the
circuit converter the four switch inputs form the Atari stick
connector to the different X and Y resistance values which are the
outputted to PC joystick port. The circuit gives the following
resistance values from the 9 different positions an Atari-style
joystick stick can have:

The resistance values are exactly the same as what is given by
PC gamepad controllers (like Gravis Gamepad for PC) or what normal
PC analogue joystick give out when it is in center position or in
any extreme position (fully moved to one of the eight main
directions).The different resistance values are generating using
following method (this example is for forward/back direction
movevement):

When the digital joystick is in center position the current
flows through R3, D1 and potentiometer. When potentiometer is tuned
center position the PC joystick interface seen around 50 kohm
resistance. No current flows through T1.

When the “‘Forward “‘switch is closed the point between R3 and
D1 is grounded. Now the current can only go to PC joystick
interface though the potentiometer, which give 100 kohm
resistance.

When “‘Forward switch is closed then current starts to
flow from T1 emitter to base and then through R2 to forward switch.
This base current causes that T1 starts to conduct from emitter to
collector so the PC joystick interface sees very low
resistance.Left/Right “‘movement conversion works in
exactly the same way. Normal digital joystick button is wired to
Button 1 input in PC joystick interface and one extra button in
digital joystick connector is wired to the Button 2 in PC joystick
interface.NOTE: The transistors and and diodes are absolutely
necessary for this circuit to work. You can”t avoid using active
circuit elements if you want to to convert and unmodified Atari
joystick to PC josytick port. I know that there are some simple
circuits which use only few resistor to adapt joystick to PC, but
those can”t be used with unmodified Atari joysticks. They require
you to completely rewire internals of the joystick (which is not
always possible as shown in their circuit diagrams). The intention
of my circuit was to make the circuit general and avoid any changes
needed inside the joystick.====Tuning the circuit====When you have
built the interface, you have to set the trimmers to correct
positions.The potentiometers must be set so that the circuit shows
50 kohm to joystick interface when the joystick is in the center
position. So first align the potentiometers just to the center
position. If you want to more accurate alignment, use a simple test
program to align those more accurately. The aligning procedure is
very simple: just urn tje joystick to left and right positions and
calculate the average of those values the test program shows. The
align the potentiometer so that the circuit gives the calculated
value when joystick is in the center position. Do the same to the
forward/back direction.====Modification idea: Getting more buttons
to work====Because the use of extra buttons in joystick is not
standarized, what pins are used on those depend on the computer, it
is possible to make a circuit which works well with all kinds of
button arrangement, you need to do some experimenting to get the
second butotn to work. If for some reason the circuit as it is does
not work, it might be possible that your joystick uses pin 9 for
extra button, instead of pin 5, you must do a small modification to
the circuit to get the system work. A simple modification is to
move the wire going to pin 5 on 9 pin connector to pin 9 on the
same connector.Another idea which you can try is to keep the wire
on pin 5, but add an extra wire which connects pin 5 and 9
together. This causes that all extra button (no matter are they
connected to pin 5 or 9) are recognized as button 2 on PC joystick
port.